The present invention relates to an improved apparatus and method for flushing the slag from and controlling the water level of a burn table for a metal cutting apparatus. More particularly, the invention pertains to a system utilizing compressed air to supply water for slag flushing and level control.
Metal cutting apparatus utilizing, for example, gas or plasma cutting torches is well known in the art. Such a metal cutting apparatus typically includes a cutting torch or gang of torches supported on a overhead carriage for programmed cutting movement over a metal workpiece supported on a so called "burn table" positioned below the carriage. The burn table, in turn, is located above a burn tank containing water into which the metal oxide slag, molten metal and small pieces of scrap fall as they are cut from the workpiece. The water level in the burn tank is commonly variable within selected limits to a maximum level in which the burn table and workpiece may be completely submerged for under water cutting. The burn tank also typically includes a downwardly sloping floor or bottom wall onto which the slag falls and moves or is caused to move downwardly for collection at the lower edge and removal.
The prior art discloses a variety of methods and related apparatus for flushing the slag from the sloping floor of a burn tank to a common lower collecting point for removal and disposal. U.S. Pat. No. 3,486,744 (Beyers et al) utilizes a pump to circulate slag flushing water to a trough at the upper edge of the inclined floor portion, from which trough the water overflows down the floor carrying with it the slag particles to a lower collecting trough. The sloping floor portion comprises two identical side floors which slope downwardly from the tank side walls to a common longitudinally-extending collecting trough in the center of the tank. Similarly, U.S. Pat. No. 3,526,395 (Brown) utilizes a recirculating pump to carry water to the upper edge of an inclined floor portion where it flows downwardly over the floor carrying slag particles to a collection point along the opposite side wall of the tank. U.S. Pat. No. 3,792,846 (Geffert) discloses a self-cleaning burn table in which slag is washed from an inclined collecting surface which is maintained under the level of water in the burn tank and from which the slag is washed by high pressure jets of water supplied by a pump to a common header.
In each of the foregoing patents, the water circulation pump may also be utilized to control and vary the level of water in the tank to accommodate various cutting processes. These water flushing, recirculation and level control systems require fairly complex plumbing systems and associated flow controls. In addition, the pumps utilized in these systems are subject to severe wear by the highly abrasive slag particles which are unavoidably circulated through the pump despite protective filters.
U.S. Pat. No. 3,743,260 (Alleman et al) shows a slag collecting tank for a burn table having downwardly sloping floor portions over which the slag moves downwardly for collection in a centrally located trough at the bottom of the tank. Supplemental water chambers below the sloping floor may be pressurized with compressed air over the water level therein to force the water into the main tank portion above the sloping floor to establish variable selected water levels in the burn tank, as may be desired. No particular means for flushing the slag from the inclined floor surface is disclosed beyond the relatively steep slope thereof to facilitate the downward movement of slag by gravity. The steep slope of the inclined floor portion requires a relatively deeper burn tank than might normally be required. U.S. Pat. No. 4,162,060 (Anderson et al) shows a burn tank in which compressed air is utilized to vary the water level in the tank as desired. However, collection of the slag from the burning process is accommodated by upwardly tilting slag-collecting subfloor portions to dump the slag thereon nto collecting bins disposed at the side of the tank. Such a slag collecting apparatus is fairly cumbersome and mechanically complex.